C1k has a link to C2j iff k = j.
The core nodes of a given region are directly connected.
Inter-region links only connect core nodes of the same plane.
{C1k has a link to C1j} iff {C2k has a link to C2j}.

It should say:

C1k has a link to C2j if k = j.
The core nodes of a given region are directly connected.
Inter-region links only connect core nodes of the same plane.
{C1k has a link to C1j} if {C2k has a link to C2j}.

Notes:

Does "iff" mean something special that is different to "if" or is this a typo? If the former, should it be called out in a glossary?
--VERIFIER NOTES--
"iff" means "if and only if"
This abreviation is part of the RFC Editor's well known ones.
Please see: https://www.rfc-editor.org/materials/abbrev.expansion.txt